Chicken immunoglobulins will be exaained as to C-region complexity, evolution, and biological function. The studies will involve chemical and immunologic analyses of the heavy and light chains of immunoglobulins isolated from the sera, egg white, and bile of chickens. Sera will also be obtained from bursectomized chickens. The major objective is to establish the degree of chicken C-region immunoglobulin complexity, i.e. gene duplications giving rise to immunoglobulin heavy and light chain C-regions and to compare the immunological and chemical data of chicken immunoglobulins with that of mammals in order to obtain information on the evolution and biological functions of the different immunoglobulins. The studies are designed to find answers to the following questions: (1) What is the extent of gene duplication giving rise to different immunoglobulin classes in chickens? (2) Has a recent gene duplication, independent of gene duplications in mammals, occurred giving rise to subclasses in chickens? (3) Are one or two genes coding for chicken light chain types/ (4) Are chicken immunoglobulin classes, homologous as to structure and function with mammalian immunoglobulin classes? Data obtained on the structures, function, and evolution of chicken immunolobulins should reveal much information about the genetic events, leading to the immunoglobulins of mammals.